The present invention relates to a cab ventilation system for an off-road work vehicle, and more particularly to control strategy for a cab ventilation system that will enhance heating capacity during low ambient temperature conditions.
Many agricultural work vehicles feature operator compartments that are enclosed with large glass or plastic panels that extend substantially the entire way around the operator. The large panels enclose the operator and protect the operator from the elements. Such operator cabs feature large internal volumes and equally expansive exterior surfaces, usually of transparent panels, which imposes additional challenges to maintaining the compartment at an comfortable temperature.
Work vehicles may have a pressurizer fan or blower which further burdens the compartment heating and cooling system. Vehicles so equipped, such as tractors or combines, generally have two blowers, one blower for pressurizing the operator compartment with outside air and the other blower for recirculating air within the operator compartment. The purpose of the pressurizer blower is to provide a slight positive pressure in the operator compartment to ensure that no air is drawn into the operator compartment through cracks or gaps in the ceiling, walls, or floor of the operator compartment. A positive pressure of about 6 to 25 mm of water is sufficient to prevent dirty, dusty air from infiltrating into the compartment, degrading air quality inhaled by the operator, dirtying the interior and possibly fouling operator controls. The work vehicle may have many small air leaks located in and around the compartment, thus the pressurizer blower may introduce a significant amount of outside air into the operator compartment in order to maintain the necessary slightly positive pressure inside the compartment.
Heating the operator compartment may be further compromised by the limited capacity of the heating source on vehicles having advance emission controls (e.g., a Tier 4 engine using selective catalytic reduction) or low horsepower engines. During compartment heating operations when the ambient temperature is very low, the ability of the heating system to warm the compartment air is marginal, especially soon after the engine is first started when engine coolant temperature is low. A large influx of outside air through the pressurizer blower only worsens operator compartment heating performance.
It would be a great advantage to provide an HVAC system for a work vehicle that disengages the pressurizer blower and reduces the quantity of outside air introduced into the operator compartment during low ambient temperature conditions and periods of maximum heating demand. Further advantages would be realized by a system capable of monitoring one or more vehicle and HVAC system parameters and disengaging the pressurizer blower when certain predetermined permissive conditions are satisfied. These and other objects are satisfied by the invention described below.